The present disclosure relates generally to an electrode-texturing tool and a method of use thereof, and particularly to an electrode-texturing tool for creating a textured surface at the tip of an electrode.
In resistance spot welding, pressure is applied to two or more contacting metal sheets by means of copper or copper alloy electrodes, while simultaneously passing a high electric current between the electrodes. Electrical heating causes a molten nugget to form at the sheet interface at the point of pressure. Resistance spot welding is one of the most useful and economical methods to join sheet metal components. For mass production, such as in the manufacture of automotive bodies, electrode life and equipment downtime to replace worn out electrodes is a consideration.
An aspect of resistance spot welding is the electrical resistance between the electrodes and the workpiece (electrode resistance), and between the contacting metal sheets that make up the workpiece (faying surface resistance). In the resulting series arrangement of resistances, it is desirable for the faying surface resistance to be a substantial part of the total resistance (electrode plus faying surface resistance). However, variations at the electrode-to-workpiece interface may cause the electrode resistance to vary, and in some instances to exceed a preferred level. Such variations may result from an oxide layer being present on the workpiece surface that increases the contact resistance at the electrode-to-workpiece interface. As the electrode-to-workpiece contact resistance increases, so does the heat generation in that vicinity, which may result in electrode wear at the electrode tip over time, and variations in the quality of the weld. Furthermore, the inconsistency in the nature of the surface oxide films, particularly with aluminum and magnesium alloys, can make the electrode resistance variable, resulting in erratic weld quality.
Low electrode resistance on aluminum alloy surfaces may be obtainable with abrasion or arc cleaning of the outer surfaces of the workpiece. Alternatively, the surface of the spot welding electrode may be roughened by sand-blasting or shot-peening. The sharp asperities on the roughened electrode surface can break through the insulating layers on the surface of workpiece and make direct contact with the underlying fresh metal, thus reduce the contact resistance between the electrode and the workpiece (electrode resistance) and increase the service life of the welding electrode. An added benefit of roughened electrodes is the elimination or reduction of electrode skidding.
A spot welding electrode will deteriorate over time with use, and especially quickly for welding aluminum or magnesium due to the high currents used and the metallurgical interactions between aluminum or magnesium sheet and the copper electrodes. A worn electrode must be either dressed by re-cutting the welding surface, or exchanged with a new electrode to maintain weld quality. For aluminum or magnesium alloys, this redressing is often done after only a few tens of welds. Textured or roughened electrodes improve the spot welding process significantly as mentioned above. However, the textured surface will be lost after electrode dressing.
If surface roughening is done by a method like sand-or grit-blasting, the electrode must be removed from the welding machine and the electrode tip surface roughened at a separate location, which may significantly and negatively impact the productivity. Accordingly, there is a need for an electrode texturing or roughening tool and method of use thereof that overcomes these drawbacks.